The Matroska Multimedia Container is an open standard free container format, a file format that can hold an unlimited number of video, audio, picture or subtitle tracks inside a single file. It is intended to serve as a universal format for storing common multimedia content, like movies or TV shows. Matroska is similar in concept to other containers like AVI, MP4 or ASF, but is entirely open in specification, with implementations consisting mostly of open source software. Matroska file types are .MKV for video (with subtitles and audio), .MK3D for stereoscopic video, .MKA for audio-only files and .MKS for subtitles only.
The Matroska Multimedia Container makes high definition possible by embedding the h.264 high definition encoded video, and the 5.1 (or better) Audio into a single file.
To watch MKV files either through your computer or your TV/Blu-Ray player, they must know how to understand the .mkv format, and that may require additional applications/plug-ins.
Below are a list of useful tools to help you get the best high definition experience.
Players:
VLC - http://www.videolan.org/vlc/
MPlayer - http://www.mplayerhq.hu/design7/dload.html
Media Centres:
Boxee - http://www.boxee.tv/
PS3 Media Server - http://www.ps3mediaserver.org/
XBMC - http://xbmc.org/
Codecs:
K-Lite Codec Pack - http://www.codecguide.com/download_kl.htm
Perian (Mac OSX) - http://perian.org/
